People have a hard time understanding that just because a screen might be drawn at 1080p by the host system, it doesn't improve the 480p resolution of the original graphics and some are disappointed with the outcome because the low-res images may seem 'uglier'.
In this case, the difference between the Wii and N64 was noticeable but possibly not as harshly as when in Wii mode on the Wii U.

Graphics is an overly subjective area - I wish I could find a picture of the old CRT arcade and VIC20 versions of 'driving' games when I read some of the drivel aimed at the Wii U - so your expectations will define whether it's good or bad.Best bet is to find someone you know with the VC Paper Mario on the Wii U and see for yourself.

As a side note, this is why you'll see a lot of people asking for HD rebuilds of classic games.